Electric motor control system



May 3, 1949. E. c. WAHLBERG ELECTRIC MOTOR CONTROL SYSTEM 2 Sheets-Sheet1 Filed April 28, 1945 \Qllilii R v v NFAW NJ: H

wa k a r BJ mm w of bin 53 v .25 5% Tm .55 5mm May 3, 1949. E. c.WAHLBERG ELECTRIC MOTOR CONTROL SYSTEM 2 Sheets-Sheet 2 Filed April 28,19-45 Patented May 3, 1949 ELECTRIC MOTOR CONTROL SYSTEM Eric C.Wahlberg, Stamford, Conn., asslgnor to Electrolux Corporation, OldGreenwich, Conn., a corporation of Delaware Application April 28, 1945,Serial No. 590,820-

25 Claims. (Cl. 318-437) My invention relates to an electric system andmore particularly to a system including aplurality of preferablysynchronous electric motors, each driving a gear reduction unit. Incertain applications of such a system, such as for driving scanningdiscs in television and radar equipment, it is essential that the outputshafts of the several gear units not only be driven in synchronism witheach other, but also start from certain predetermined angular positionswith respect to each other.

In my Patents Nos. 2,399,272 and 2,399,273, both granted on April 30,1946, as well as in Patent No. 2,360,856, granted October 24, 1944 to F.C. Doughman and myself, there are shown systems including a plurality ofelectric motors with means for causing the motor shafts to be angularlypositioned before starting, and to start, run and stop in synchronism.Such a system would be ideal for operating scanning discs, provided thediscs could be directly driven by the motor shafts without any gearreduction, inasmuch as the shafts may be angularly aligned before themotors are started. However, the low speed at which it is necessary torotate scanning discs makes it impractical to drive them directly, andhence, gear reduction units are necessary, and if the armature shaft ofone motor makes a different number of revolutions than the shafts of theother motors, the output shafts of the gear units will not be in properangular alignment, even though the armature shafts themselves areproperly aligned.

It has been found in practice that, with motors of this type, the shaftof one motor may occasionally during stopping make one revolution moreor less than the shafts of the other motors. For most applications wheredirect drive is possible this is of no importance, inasmuch as theshafts are brought into proper alignment each time the motors arestarted, and even for applications involving gear reductions, it usuallyis of but minor moment, because the occasional over or under runs of onerevolution are apt to compensate and cancel out rather than accumulate,and hence if absolute angular positioning of the output shafts at alltimes is not essential, such a system will operate entirelysatisfactorily if the angular positions of the output shafts areoccasionally checked and if necessary, the output shafts realignedmanually.

However, scanning discs must be perfectly aligned at all times duringoperation, and it is the object of my present invention to provide meansfor automatically obtaining such alignment of Fig. 1 is a wiring diagramshowing one embodiment of my invention, and

Fig. 2 is .a wiring diagram of another embodiment, particularly adaptedfor use in a system in which one of the motors drives a substantiallygreater load than the other.

Referring to Fig. 1, reference character 10 designates a conductor whichis connected to one side of any suitable source of electric current, theother side of which is grounded. Conductor I0 is connected through amanually operable switch l2 with a conductor H. A conductor l6 connectsconductor [4 with a contact arm of a magnetic relay designated generallyby reference character A. This relay is provided with two contact armswhich cooperate with normally open contacts A1 and A3, and normallyclosed contacts A2 and A4. Contact A: is connected by means of aconductor I8 with the rotary element 20 of a rotary switch designatedgenerally by reference character 22. The stationary element of thisswitch comprises a large segment 24 and a small segment 26. The rotaryelement 20 is mounted to be driven at a one to one ratio by the outputshaft 28 of a gear reduction unit 30.

This gear unit is driven by the armature shaft 32 of an electric motordesignated generally by reference character I. This motor includes anarmature diagrammatically shown at 34 which has the usual commutatorcooperating with brushes 36 and 38, and a field winding 40. The armaturealso includes a pair of slip rings 42 and 44 which are connected tospaced points in the armature winding, in the manner particularlydisclosed in my aforesaid Patent No. 2,399,273.

The larger segment 24 of rotary switch 22 is connected by means of aconductor 46 with one side of the solenoid of a magnetic relay 0, theother side of which is grounded. This relay has a single contact armwhich cooperates with a normally open contact C1 and a normally closedcontact C2. Contact C1 is connected through a resistance R and aconductor 48 with the conductor H. The contact arm of relay C isconnected through a conductor ill with the brush 35 of motor I. ContactC: is connected through a conductor with the arm oi relay A whichcooperates with contacts A: and A4. Contact A4 is connected through aconductor 52 with the commutator brush 3| of motor I as well as withcorresponding brushes ill and ll" of similar motors II and III.

The smaller segment 20 of the switch 22 is connected through a conductorI4 to the rotating element 20 of a rotary switch 22', which element isdriven at a one to one ratio by the output shaft 28' of gear reductionunit 30' which is driven by motor II. The larger segment 24' of switch22' is connected through a conductor 56 with one side of the solenoid ora magnetic relay D, the other side or which is grounded. This relay hasa single contact arm which cooperates with a normally open contact Drand a normally closed contact Dr. The contact arm is connected through aconductor 30 with the commutator brush 36' of motor II. Contact Dr isconnected through resistance R and conductor 48 with the line I, whilecontact Dr is connected to conductor 5 l The smaller segment 20' ofswitch 22' is connected through a conductor OI with the rotating element20" of a rotary switch 22". This rotary element is driven at a one toone ratio by the output shaft or a gear reduction unit 30" driven by themotor III. The larger segment 24" is connected through conductor 2 withone side of the solenoid of a relay E, the other side e which isconnected to conductor I I.

One side or each field winding of the motor is grounded, while the otherside or each winding is connected through conductor II with conductorII. The corresponding slip rings of the motors are connected in parallelby means of conductors l2 and II, which conductors are also connected tonormally open contacts 131 and B5, respectively, or a magnetic relay B.The contact arm of this relay which cooperates with contact B3 isconnected through conductors Ii and 48 to the line ll, while the contactarm which cooperates with contact Be is grounded.

The smaller segment 2!." or switch 22" is connected through a conductorII with one side of the solenoid of a flux decay relay F, the other sideof which is grounded. As is well known, a relay 0! this type picks upits contact arm as soon as the solenoid is supplied with current, butcontinues to hold the arm for a predetermined length of time after thesupply or current to the solenoid is interrupted. Relay F has a singlecontact arm which cooperates with a normally open contact F1. The arm isconnected to conductor ll while the contact F1 is connected throughconductor I with one side of the solenoid of magnetic relay B, the otherside of which is grounded.

Cont-act B1 is connected through conductors 8i and 48 with conductor ll,while the contact arm which cooperates with B1 is connected throughconductor I3 with one side of the solenoid oi relay A, the other side01' which is grounded. Contact A1 is also connected to conductor 83,thus providing a holding circuit {or this relay.

As previously stated, the normally open contacts B: and B5 are connectedto conductors 12 and I4. Normally closed contact B4 is connected througha conductor 84 with the normally open contact A1, while the normallyclosed contact Be is connected through conductor 52 to the com mutatorbrushes 3!, II, and ll" of the motors.

The above described device operates as follows:

With the switch 12 open, all of the relays will occupy the deenergizedpositions shown in the wiring diagram, and all the circuits will beopen.

It will first be assumed that several motors have stopped with rotatingelements 10, 20', and 20" of the respective switches in contact with thelarger segments 24, 24, and II". In all probability, the output shai'tor the several gear units will be in substantially angular alignment,but they may not be in exact alignment. When switch I2 is closed itsupplies excitation current to the field winding ll, 40, and 40" throughconnected conductors I4 and 48. When the switch I2 is closed it alsocompletes a circuit through conductor ll, normally closed contact A2,conductor l8, switch element 20, larger segment 24 and conductor 4 toenergize relay C, which consequently opens contact C2 and closes C1.Closing of contact Ci connects brush 36 of motor I with conductor 14through conductor ill. resistance R and conductor 48. Inasmuch as theother brush II of motor I is connected to ground through conductor 52and contact Be. the armature b supplied with current which. however, dueto resistance R is at lower than line voltage. Hence, the motor Ioperates at reduced speed, thus rotating switch element Ill through gearreduction 30 until the element Ill leaves the larger segment 24 andmakes contact with smaller segment 25. Operation of the motors atreduced speed during positioning is desirable ior .two reasons. In thefirst place, it tends to prevent overtravel of the element 20, and inthe second place it makes it possible to operate motor I while theremaining motors are stationary without necessitating opening thecircuits between the slip rings of the various motors. Inasmuch as thefields of all the motors are excited the armatures of motors II and IIIwould tend to follow the armature of motor I even at this reduced speedof operation, but they are prevented from doing so because thecommutator brushes are short circuited. Thus, brush N is connectedthrough conductor 58, contact Dz, conductor 5|, contact A4, andconductor 52 with brush 3| oi the same motor. In similar manner brushesIt" and 3| of motor III are short circuited through contact E2.

As soon as element 20 leaves segment 24, relay C is deenergized, therebyopening contact Cl so as to interrupt the supply 01' armature current.and closing contact C: so as to short circuit the armature of motor I.Inasmuch as field ll remains excited, the motor is dynamically braked soas to stop almost instantaneously which, coupled with the fact that themotor was operating at reduced speed, effectively prevents anyovertravel and precisely indexes the angular position or the outputshaft 28.

When therotating element II of switch 22 contacts the smaller segment 2a circuit is established from conductor ll through conductor l6, contactA2, conductor II, element 20, segment 26, conductor 54, element 2|,segment 24', and conductor N to energize the solenoid of the relay D.This causes motor II to operate in a manner similar to that described inconnection with motor I until element leaves segment 24' and contactssegment 28'. Motor II is then almost instantaneously stopped so as toindex the output shaft 23' in proper angular position.

The circuit previously traced from conductor II to element 20 is thencontinued through segment 26', conductor 30, rotary element 20", segment24" and conductor 62 to energize relay E. This results in the operationof motor III in the same manner as previously described until the switchelement 20" leaves segment 24" and contacts segment 26", whereupon themotor is stopped. Consequently, all of the output shafts of the gearreduction units have been turned to exactly the same angular position.

When the switch element 20" contacts switch element 26" the circuitpreviously traced from conductor i4 is continued through conductor 18 soas to energize relay F. This closes contact F1, thus energizing relay Bfrom conductor ll through conductor 80. Closing of contact 133 connectsthe slip rings 42, 42', and 42" to the line in through conductors I2,16, and 48, while closing of contact B5 connects slip rings 44, H, andM" to ground through conductor 14. Thus, the slip rings are connected inparallel across the power supply, while the opening of contacts B4 andBa maintains the armature brushes disconnected from the power supply. Asis explained in my aforesaid patents, supplying current from the line tothe slip rings, produces fixed magnetic poles in the armatures whichcause the armatures to line up in predetermined angular positions withrespect to their stationary fields and hence, with respect to eachother. This positioning of the armature shafts is preferable, eventhough the output shafts of the gear units have been positioned because,if the gear ratio is high, the output shafts may not be indexed orpositioned precisely enough to accurately align the armature shafts, andit is characteristic of mo tors of this type that if their armatureshafts are not properly aligned before starting, they may be subjectwhen started to undesirable hunting before they come into synchronism.

Clcming of contact Bl supplies current through conductors I4, 48, M and83 to energize relay A. Closure of contact A1 provides a holding circuitthrough conductor l6 for relay A, and consequently this relay remainsenergized as long as switch l2 remains closed even though contact F1 isopen. This contact will open because the circuit from conductor 14 tothe solenoid of relay F is interrupted by the opening of A2. However,contact F1 does not immediately open, due to the time delaycharacteristic of the relay F, but remains closed long enough to permitpositioning of the armatures and to assure that contact A1 will beclosed to provide for the aforesaid holding circuit of the A relay.Closure of contact A: has no immediate effect inasmuch as contact B4 isopen, while opening of contact A4 removes the short circuit of thecommutator brushes.

Upon the lapse of a predetermined interval, usually a few seconds,following the interruption of the circuit to the solenoid of the fluxdecay relay F by the opening of contact Ah, the contact F1 opens so asto deenergize relay B. This opens contacts Ba and B5 so as to disconnectthe slip rings from the line l0 and ground, respectively. Contact B1 isalso opened, but this does not drop out the A relay, because its ownhold-- log circuit is closed through contact A1. Contacts B4 and B0 areclosed by the deenergization of solenoid B with the result thatconductor ii is connected to the line i0 through contact Aa, conductor34, contact B4, and conductors II and I3. Inasmuch as commutator brushes33, 30, and 36" are connected to conductor it through contacts C2, D2,and E2, respectively, these brushes are now connected to the line, whilebrushes 38, 38', and 38" are grounded through conductor 52 and contactBe. The armatures are hence connected in parallel across the powersupply and, therefore, the motors start and run. During starting andrunning the motors are held in synchronism with respect to each other byvirtue of the tie provided by the conductors l2 and 14 between the sliprings as is clearly explained in my aforesaid patents. Inasmuch as themotors operate in synchronism, their output shafts 28, 28, and 28" willlikewise rotate in synchronism and hence, scanning discs or the likedriven thereby will be maintained in synchronism.

The motors operate in this manner as long as desired and may be stoppedby merely opening the switch I 2. Opening of this switch interrupts thesupply of current to the relay A, thus opening contacts A1 and As, andclosing contacts A: and A4. Opening of A1 merely opens the holdingcircuit for relay A, thus conditioning this circuit for the nextstarting. Opening of contact A: interrupts the supply of current fromthe line ID to the brushes 36, 36', and 38" of the motors. Closure ofcontact A: completes the circuit from conductor I4 through the rotaryelement 20 of switch 22 but this has no eiIect as the switch I2 is openand hence conductor I4 is disconnected from the line. Closure of contactA4 short circuits the armatures, inasmuch as the brushes 38, 38', and38" are connected through the conductor 52, contact A4, conductor 5|,and contacts C2, D2, and E2, and conductors 50, 53, and 84,respectively, with the brushes 36, 36, and 36". This establishes thedynamic braking circuits previously described.

In the event that the motors should be stopped with all of the rotaryelements 20, 20', and 20" in contact with the smaller segments 26, 26,and 26", respectively, th next time the switch I2 is closed relay Fwould be immediately energized and the armature shafts would be.positioned, and the motors would start and run in synchronism withoutany preliminary positioning of the output shafts. This is entirelysatisfactory, inasmuch as the fact that the rotating elements are all incontact with the smaller segments indicates that the output shafts wereproperly indexed when the motors stopped.

If one or more but not all of the rotating elements are in contact withthe respective smaller segments, the indexing operation of output shaftsdriving such elements will be omitted, while the remaining output shaftswill be indexed in the manner first described, whereafter all thearmatur shafts will be positioned and the motors will start and run insynchronism. It will thus be seen that, regardless of the angularpositions in which the output shafts may come to rest whenever themotors are stopped, these shafts will be automatically alignedimmediately before the motors are next started.

In certain applications of the above described A system, notably foroperating radar equipment,

driven by the remaining motors, and it has been found that after theoutput shafts have been properly positioned, diificulty is experiencedin starting the several motors in synchronism. Due to the relativelygreater inertia load carried byone of the motors, this motor tends tolag behind the others, thus causing undesirable hunting before themotors get into synchronism.

The system shown in Fig. 2 overcomes this difficulty. In this system themotors are individually positioned as before, the motor driving theinertia load being the last to be positioned. Moreover, a higher voltageis used for driving this last motor during positioning than is impressedon the normally loaded motors, and when the output shaft of the lastmotor has been positioned, the remaining motors are started withoutstopping the last motor. Thus the inertia load of the last motor hasbeen largely overcome at the instant when the motors are started insynchronism, and consequently hunting is avoided.

Referring to Fig. 2 reference character I designates a line conductorwhich is connected through a manually operable switch I2 to a conductorI4. Conductor I6 connects conductor It with the contact arm of amagnetic relay G which arm cooperates with contacts G1 and G1. ContactG2 is connected through the conductor I8 with the rotary element 20 ofthe rotary switch 22. As was described in connection with Fig. 1, thisswitch includes a large segment 24 and a small segment 25. The rotaryelement is driven by the output shaft 28 of a gear reduction unit 30which is driven by the armature shaft 32 of the motor I. This motor hascommutator brushes 36 and 38, and slip rings 42 and 44 connected tospaced points in the armature winding.

The field is connected to the conductor I4 through conductor 48.

The larger segment 24 of the rotary switch is connected throughconductor 46 with the solenoid of a magnetic relay H having a singlecontact arm cooperating with contacts Hi and H2. The arm is connectedthrough conductor 50 with the brush 36 of motor I, while contact H1 isconnected through resistance R and conductor 48 with conductor I4. Thecontact H2 is connected through conductor 5| with the contact arm ofrelay G which cooperates with contacts G5 and Ge. Contact G6 isconnected through a conductor 52 with the brush 38 of motor I, as wellas with the corresponding brushes of the remaining motors. Conductor 52is also permanently connected to ground. Contact G5 is connected througha conductor 94 with conductor II.

The smaller segment of switch 22 is connected by means of a conductor 54with the rotary elemer 20 of the switch 22. This rotary element isdriven by the output shaft 28 or the gear unit so which is driven by themotor II. The larger segment 24' of the switch is connected throughconductor 58 with the solenoid of a magnetic relay I having a contactarm cooperating with contacts I1 and I2. The arm is connected by aconductor 58 with a brush 36' of the motor II. Contact I1 is connectedthrough resistance R and. conductor 48 with conductor I4 while contactI: is connected to conductor 5i.

The smaller segment 26' of switch 22 is connected through conductor 60with the rotary element 20" of the switch 22". This rotary element isdriven by the output shaft 28" of the gear unit 30". The shaft alsodrives a load I00, designated on the drawing as an inertia load, whichis substantially greater than the loads driven by the other outputshafts. The larger segment 24" is connected through conductor 82 withthe solenoid of a relay J having a contact arm cooperating with contactsJ1 and Jr. The arm is connected through conductor with brush 88" ofmotor III. Contact J: is connected to conduotor SI, and contact J1 isconnected through a conductor I02 with an adjustable contact I08 on theresistance R. Corresponding slip rings of the several motors areconnected in parallel by means of th conductors 12 and II.

The smaller segment 26" of switch 22" is connected through conductor I8to the blade or other movable member of a single pole, double throwswitch I08 having contacts I08 and H0. Contact I08 is connected to thesolenoid of a flux decay relay K having a single contact arm whichcooperates with a normally open contact K1. This contact is connected bymeans of a conductor 80 with the solenoid of relay G and also withcontact G1. The arm 01 relay K is connected to conductor I4.

Contact III! of switch I00 is connected through a conductor 2 withconductor 80 and a suitable audible, visible or other signal device,such as the lamp Ill, is interposed in conductor 2. Relay G has acontact arm which is grounded and which cooperates with the normallyopen contact G3, which contact is connected to conductor I8.

The above described system operates as follows:

In starting, the switch I08 should be closed in its upper position so asto connect conductor ll through contact I08 with the solenoid of relayK. Switch I2 is then closed, whereupon current flows through conductorsII and I8, contact G2, and conductor I8 to the rotary element 20 oiswitch 22. If this element is in contact with segment 24, the circuit iscompleted through this segment and conductor 48 to the solenoid of relaiH. This relay is actuated so as to open contact H2 and close contact Hi.Consequently, brush 80 or motor I is connected through conductor 50,contact H1, resistance R, and conductor 88 with conductor I4. Inasmuchas the other brush is permanently connected through conductor 52 withground, the motor I is caused to operate and will run at a reduced speedbecause of the inclusion of resistance R in its armature circuit.Contact 20 is thus driven until it leaves segment 2| and contactssegment 26. When this occurs, the circuit to relay H is open, andconsequently contact H1 opens and contact Hz closes. Opening of contactHi interrupts the supply or current to the armature while closing ofcontact H: short circuits the armature, inasmuch as brush 86 isconnected through conductor 50, contact H2, conductor 5|, contact Go,and conductor 52 with the other brush 38. Hence, this motor isdynamically braked so as to prevent the possibility of overtravel of therotary element 20.

When this element contacts segment 26 the circuit is completed throughconductor 54, rotary element 20', segment 24', and conductor 56 to relayI. Actuation of this relay drives motor II at a reduced speed in thesame manner as described in connection with motor I. When element 20'leaves segment 28' and contacts 28', motor II is stopped and dynamicallybraked.

When smaller segment 26' is contacted by the element, the circuit iscompleted through conductor 60, rotary element 20", segment 24", andconductor 62 to relay J. Actuation or this relay closes contact J1 andopens contact J2. Closing occurs the relay J is deenergized but theclosing of contact J: does not dynamically brake motor III because thecircuit across the brushes l and 38" is simultaneously opened at contactGo, as will be explained. When rotary element 20" contacts segment 20",the circuit is completed through conductor and contact I08 of switch I00to the solenoid oi relay K, thus closing the contact K1. This connectsthe solenoid of relay G to conductor I through conductor 80 and contactK1, thus energizing relay G. This results in the opening of contact G:and the closing of G1, the latter contact providing a holding circuitfor the relay G. Opening of contact G: opens the circuit to the solenoidof relay K, but the time delay characteristic of this relay causes it tohold long enough to insure that contact G1 will be closed.

Actuation of the G relay opens contact Gs so as to remove the shortcircuit across the armature brushes of the several motors, while theclosing of contact G5 connects conductor ii to conductor 04 and hence,to conductor I4. Thus, full line voltage is supplied from conductor I4through contacts H2, I2, and J: to the brushes 36, 30', and 30' of theseveral motors. Hence, motors I and 11 start while motor III is stillrunning and therefore, this latter motor does not have to pick up itsinertia load during the synchronous starting of the motors. As a result,all of the motors are able to start and run in synchronism withoutobiectional hunting.

If it is desired to ascertain definitely that the various output shaftsare operating in proper angular phase relationship, the switch I05 maybe closed in its lower position so as to connect conductor I8 throughcontact IIO with conductor IIZ. This establishes a circuit fromconductor I4 through conductor I6, contact G1, conductor 80, lamp I,switch I06, and conductor Iii to the smaller segment 26" of rotaryswitch 22". While the rotary elements of the several switches are incontact with the larger segments, this circuit will not be completed toground, but if each of the rotary elements contacts the respectivesmaller segments simultaneously the circuit will be'completed fromsegment 26" through rotary element 20", conductor 00, segment 26',rotary element 20, conductor 04, segment 26, element 20, conductor I8,and contact G3 to ground. This will cause the lamp Ill to light as longas all of the rotary elements are in contact with the respective smallersegments. However, if one or more of the output'shaits isout of properangular phase relationship, all of the rotary elements will not contacttheir respective smaller segments at the same time andthe lamp II willnot light. Consequently, ii whenthe switch I06 is closed in its lowerposition the lamp II 4 lights periodically it indicates that the outputshafts are in proper angular phase relationship, while if it fails tolight, it indicates that this relationship does not obtain. In thelatter event, the operator should shut down the sytem by opening switch"tem could be employed in connection with the circuit shown in Fig. iand in most instances it would be highly desirable. However, it isparticularly desirable in connection with the system shown'in Fig. 2 forthe reason now to be described. Should it occur that all oi the motorsshould stop with the rotary elements in contact with the smallersegments of the rotary switches, when they are next started up again allor the armaturewould be immediately and simultaneously connected acrossthe line and hence, they would. all have to start from standstilltogether and without the motor III having had the opportunity toovercome its inertia load during the positioning step. Consequently, themotors would be likely to hunt during starting, and before settling downto synchronous operation the motors might make diflerent numbers ofrevolutions so that their output shafts would not be in proper angularphase relationship with each other. However, this would be immediatelyapparent through the failure of the lamp Ill to light periodically uponthe closing of switch I08 in its lower position, whereupon the operatorshould shut down the system and start it up again. Inasmuch as the.smaller segments of the rotary switches subtend arcs of only about 5,which is of a circle, the chances of the rotary element stopping on thesmaller segments is only one in seventy-two. Hence, it would not belikely for them to stop on the smaller segments twice in'succession, butit they did it would only be necessary to stop and start the systemagain.

No harm would be done it the operator attempted to start the system withthe switch I06 in its lowermost position. 'II this occurred, the motorsI and II would be operated so as to properly position their outputshafts, but when the output shaft of the motor III were turned to bringthe rotary element .20" into contact with the segment 20", the circuitfrom the line would be completed through conductor 18, contact IIIL',switch. I06, conductor II2, lamp Ill, conductor 00, and the solenoid ofrelay G to ground. Thus, the lamp I I4 and the-solenoid of relay G wouldbe in series. This would cause the lamp to glow steadily, but dimlywhile the voltage available at the relay G probably would not besuificient to actuate this relay, or if it was, contact G2 would beopened to interrupt the circuit through the rotary switches before thecontact G1 could close to provide a holding circuit, and the con tactarms of therelay G would vibrate like a buzzer and the lamp I wouldflicker. Thus, either a steady dim glow or a rapid flicker of the lampIII indicates that the switch I06 is in the wrong positionduringstarting and hence, the operator should shut the system down and thenstart it up again with the switch I06 in the proper position. 1

In both systems I have shown three motors, but obviously a smaller orgreater number could be connected in the same manner. Also, forsimplicity I have shownthe motors and relays as being supplied from thesame some of current, but this 01 course, is not necessary and separatesources could; be employed.

While I have shown and described two more or less specific embodimentsof my invention it is to be understood that this has been done for thepurpose of illustration only, and that the scope of my invention is notto be limited thereby, but is to be determined from the appended claims.

What I claim is:

1. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, individual automatic means responsive to actuation of saidswitchin means for operating each of said motors individually andnon-synchronously until said output shafts are turned to predeterminedangular positions, and automatic means for thereafter operating saidmotors in synchronism.

2. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, individual automatic means responsive to actuation of saidswitching means for starting each of said motors individually, means forstopping each of said motors when the output shaft of the respectivegear unit has been turned to a predetermined angular position, andautomatic means for thereafter operating said motors in synchronism.

3. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, individual automatic means responsive to actuation of saidswitching means for supplying current to each of said motorsindividually to cause the motors to run, means responsive to the turningof the output shaft of each gear unit to a predetermined angularposition for interrupting the supply of current to the respective motorand for dynamically said respective motor, and means operative when allof said output shafts have been turned to the predetermined angularpositions for operating said motors in synchronism.

i. In electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource electric current, switching means for controlling said current,individual automatic means responsive to actuation of said switchingmeans for operating said motors individually and in sequence until theoutput shaft of each gear unit is turned to a predetermined angularposin, and automatic means for thereafter operating said motors insynchronism.

In an electrical system, a plurality of electric motors, gear reductionunit driven by each motor, each unit having an output shaft, a sourceelectric current, switching means for controlling said current,individual automatic means responsive to actuation of said switchingmeans for operating each of said motors individually said output shaftsare turned to a predetermined angular position, automatic means forthereafter turning the armature of said motors to predeterminedangularpositions, and automatic means for thereafter starting and running saidmotors in synchronism.

6. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, individual automatic means responsive to actuation of saidswitching means for supplying current to each of said motorsindividually to cause the motors to run, means responsive to the turningof the output shaft of each gear unit to a predetermined angularposition for interrupting the supply of current to the respective motorand for dynamically braking said respective motor, automatic means forthereafter turning the armatures of said motors to predetermined angularpositions, and automatic means for thereafter starting and running saidmotors in synchronism.

7. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, individual automatic means responsive to actuation of saidswitching means for operating each of said motors individually and atnon-synchronous reduced speed until said output shafts are turned topredetermined angular positions, and automatic means for thereafteroperating said motors in synchronism at normal speed.

8. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, individual automatic means responsive to actuation of saidswitching means for starting each of said motors individually andrunning it at a reduced speed, means for stopping each of said motorswhen the output shaft of the respective gear unit has been turned to apredetermined angular position, and automatic means for thereafteroperating said motors in synchronism at normal speed.

9. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, automatic means responsive to actuation of said switching meansfor supplying current to each of said motors individually and at avoltage less than the normal voltage of said source to cause the motorsto run at reduced speed, means responsive to the turning of the outputshaft of each gear unit to a predetermined angular position forinterrupting the supply of current to the rmpective motor, and meansoperative when all of said output shafts have been turned to thepredetermined angular positions for supplying current at full normalvoltage to all of said motors for operating them at normal speed.

10. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, automatic means responsive to actuation of said switching meansfor supplying current to each of said motors individually and at avoltage less than that of said source to cause the motors to run atreduced speed, means responsive to the turning of the output shaft ofeach gear unit to a predetermined angular position for interrupting thesupply of current to the respective motor, and for dynamically brakingsaid respective motor, and means operative when all of said outputshafts have been turned to the predetermined angular positions forsupplying current at full voltage to all of said motors for operatingthem at normal speed.

11. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, individual automatic means responsive to actuation of saidswitching means for operating each of said motors individually and insequence at a reduced speed until the output shaft of each gear unit isturned to a predetermined angular position, and automatic means forthereafter operating said motors in synchronism at normal speed.

12. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controling said current,individual automatic means responsive to actuation of said switchingmeans for operating each of said motors individually and at reducedspeed until said output shafts are turned to predetermined angularpositions, automatic means for thereafter turning the armatures of saidmotors to predetermined angular position, and automatic means forthereafter starting and running said motors in syrichronism at normalspeed.

13. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, asource of electric current, switching means for controlling saidcurrent, automatic means responsive to actuation of said switching meansfor supplying current to each of said motors individually and at avoltage leSs than the normal voltage of said source to cause the motorsto run at reduced speed, means responsive to the turning of the outputshaft of each gear unit to a predetermined angular position forinterrupting the supply of current to the respective motor, and fordynamically braking said respective motor, means operative when all ofsaid output shafts have been turned to the predetermined angularpositions for turning the armatures of said motors to predeterminedangular positions and means for thereafter supplying current at fullnormal voltage to all of said motors for operating them at normal speed.

14. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, arotary switch driven by each output shaft, each switch including arotary element cooperating with a large segment and a small segment,relay means responsive to the completion of a circuit through the rotaryelement and large segment of each switch for operating the respectivemotor independently of the remaining motors until the circult isinterrupted by the rotary element leaving the large segment andcontacting the small segment, a circuit completed when the rotaryelements are in contact with the small segments in all said switches,and relay means responsive to completion of the last-mentioned circuitfor operating all of said motors in synchronism.

15. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, arotary switch driven by each output shaft, each switch including arotary element cooperating with a large segment and a small segment, asource of electric current, a resistance, relay means responsive to thecompletion of a circuit through the rotary element and large segment ofeach switch for connecting the respective motor to said source ofcurrent through said resistance for operatingsaid respective motor at areduced speed and independently of the remaining motors until thecircuit is interrupted by the rotary element leaving the large segmentand contacting the small segment, a circuit'completed when the rotaryelel4 7 ments are in contact with the small segments in all saidswitches, and relay means responsive to completion of the last-mentionedcircuit for connecting all of said motors directly to said source ofcurrent.

16. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, arotary switch driven by each output shaft, each switch including arotary element cooperating with a large segment and a small segment,relay means responsive to the completion of a circuit through the rotaryelement and large segment of each switch for operating the respectivemotor inde. pendently of the remaining motors until the circuit isinterrupted by the rotary element leaving the large segment andcontacting the small seg ment, a circuit completed when the rotaryelements are in contact with the small segments in all said switches, atime delay relay actuated by the completion of the last-mentionedcircuit,-and relay means controlled by said time delay relay for firstpositioning the armatures of said motors in predetermined angularpositions and thereafter operating all of said motors in synchronism.

17. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft,each switch including a rotary element cooperating with a large segmentand a small segment, a source of electric current, a resistance, relaymeans responsive to the completion of a circuit through the rotaryelement and large segment of each switch for connecting the respectivemotor tosaid source of current through said resistance for operatingsaid respective motor at a reduced speed and independently of theremaining motors until the circuit is interrupted by the rotary elementleaving the large segment and contacting the small segment, a circuitcompleted when the rotary elements are in contact with the smallsegments in all said switches, a pair of slip rings connected to spacedpoints in the armature of each motor, a time delay relay actuated .bythe completion of the last-mentioned circuit, and relay means controlledby said time delay relay for first directly connecting said slip ringsto said source of current and thereafter directly connecting saidcommutators to said source of current.

18. In an electric system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft,one of said motors driving a substantially greater load than theremainder of said motors, a source of electric current, switching meansfor controlling said current, individual automatic means responsive toactuation of said switching means for operating said motors individuallyand in sequence until the output shaft of each gear unit is turned to apredetermined angular position, the last motor to be operated in saidsequence being said one motor, and means responsive to the positioningof the output shaft of the gear unit driven by said one motor forstarting the remainder of said motors and for continuing the operationof said one motor.

19. In an electric system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft,one of said motors driving a substantially greater load than theremainder of said motors, a source of electric current, switching meansfor .controlling said current, individual automatic means responsive toactuation of said switching means for operating said remainder of themotors individually until the output shaft of each gear unit driventhereby is turned to a predetermined angular position, means responsiveto the positioning of the shafts of the gear units driven by saidremainder of the motors for operating said one motor to turn the outputshaft of the gear unit driven thereby to a predetermined angularposition, and means responsive to the positioning of the lastmentionedshaft for starting said remainder of the motors and for continuing theoperation of said one motor.

20. In an electric system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft,one of said motors driving a substantially greater load than theremainder of said motors, a source of electric current, switching meansfor controlling said current, automatic means responsive to actuation ofsaid switching means for operating said remainder of the motorsindividually and at reduced voltage until the output shaft of each gearunit driven thereby is turned to a predetermined angular position, meansresponsive to the positioning of the shafts of the gear units driven bysaid remainder of the motors for operating said one motor at a voltagehigher than said reduced voltage to turn the output shaft of the gearunit driven thereby to a predetermined angular position, and meansresponsive to the positioning of the last-mentioned shaft for supplyingnormal voltage to all of said motors to thereby start said remainder ofthe motors and to continue the operation of said one motor.

.21. in an electric system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft,one of said motors driving a substantially greater load than theremainder of said motors, a source of electric current, switching meansfor controlling said current, automatic means responsive to actuation ofsaid switching means for supplying current to said. remainder of themotors to cause the latter to run independently of each other, meansesponsive to the turning of the output shaft of ach gear unit driven bysaid remainder of the -otors to a predetermined angular position forriterrupting the supply of current to the respective motor and fordynamically braking said respective motor, means operative when all ofthe output shafts of said remainder of the motors have been turned tothe predetermined angular positions for operating said one motor to turnthe output shaft of the gear unit driven thereby to a predeterminedangular position, and means responsive to the positioning of thelast-mentioned shaft for starting said remainder of the motors andcontinuing the operation of said one motor.

22. In an electric system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft,one of said motors driving a substantially greater load than theremainder of said motors, a source of electric current, switching meansfor controlling said current, automatic means responsive to actuation ofsaid switching means for supplying current at a reduced voltage to saidremainder of the motors to cause the latter to run independently of eachother and at reduced speed, means responsive to the turning of theoutput shaft of each gear unit driven by said remainder of the motors toa predetermined angular position for interrupting the supply of currentto the respective motor and for dynamically braking said respectivemotor,

means operative when all of the output shafts of said remainder of themotors have been turned to the predetermined angular positions forsupplying current at a voltage higher than said reduced voltage to saidone motor to cause the latter to turn the output shaft of the gear unitdriven thereby to a predetermined angular position, and means responsiveto the positioning of the lastmentioned shaft for supplying current atnormal voltage to all of said motors to thereby start said remainder ofthe motors and to continue the operation of said one motor.

23. In an electric system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft,one of said motors driving a substantially greater load than theremainder of said motors, a source of electric current, switching meansfor controlling said current, automatic means responsive to actuation ofsaid switching means for operating said remainder of the motorsindividually and at reduced voltage until the output shaft of each gearunit driven thereby is turned to a predetermined angular position, meansresponsive to the positioning of the shafts of the gear units driven bysaid remainder of the motors for operating said one motor at a voltagehigher than said reduced voltage to turn the output shaft of the gearunit driven thereby to a predetermined angular position, means forvarying the value of said higher voltage, and means responsive to thepositioning of the last-mentioned shaft for supplying normal voltage toall of said motors for starting said remainder of the motors and forcontinuing the operation of said one motor.

24. In an electrical system, a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, arotary switch driven by each output shaft, each switch including arotary element cooperating with a large segment and a small segment,relay means responsive to the completion of a circuit through the rotaryelement and large segment of each switch for operating the respectivemotor independently of the remaining motors until the circuit isinterrupted by the rotary element leaving the large segment andcontacting the small segment, a circuit completed when the rotaryelements are in contact with the small segments in all said switches,relay means responsive to completion of the last-mentioned circuit foroperating all of said motors in synchronism, and means for connecting asignal device into said last-mentioned circuit so as to be actuated bythe completion of said circuit during operation of the motors each timesaid rotary elements simultaneously contact the respective smallsegments.

25. In an electrical system,'a plurality of electric motors, a gearreduction unit driven by each motor, each unit having an output shaft, arotary switch driven by each output shaft, each switch including arotary element cooperating with a large segment and a small segment,relay means responsive to the completion of a circuit through the rotaryelement, and large segment of each switch for operating the respectivemotor independently of the remaining motors until the circuit isinterrupted by the rotary element leaving the large segment andcontacting the small segment, a circuit completed when the rotaryelements are in contact with the small segments in all said switches,relay means responsive to completion of the last-mentioned circuit foroperating all of said motors in synchronism, and for deenergizing saidlast-mentioned circuit, an elect7 tric signal device, and means forconnecting said device to a source of current through said lastmentionedcircuit so said device will be actuated by the completion oi saidcircuit during operation of the motors each time said rotary elementssimultaneously contact the respective small segments.

ERIC C. WAHIBERG.

REFERENCES CITED The following references are of record inthe tile ofthis patent:

5 FOREIGN PA'I'ENTB Number Country Date 404,047 Great Britain Jan. 11,1934

